The present invention relates generally to optical communication systems and more particularly, to micro-electro-mechanical optical devices.
Optical communication systems typically include a variety of optical devices (e. g., light sources, photodetectors, switches, attenuators, mirrors, amplifiers, and filters). The optical devices transmit, modify, or detect optical signals in the optical communications systems. Some optical devices are coupled to micro-electro-mechanical structures (e. g., thermal actuators) forming a micro-electro-mechanical optical device. The term micro-electro-mechanical structure as used in this disclosure refers to a microscopic structure which moves mechanically under the control of an electrical signal.
Cowan, William D., et al., xe2x80x9cVertical Thermal Actuators for Micro-Opto-Electro-Mechanical Systemsxe2x80x9d, SPIE, Vol. 3226, pp. 137-146 (1997), describes a micro-electro-mechanical structure useful for moving optical devices. In Cowan et al., the micro-electro-mechanical structure is a thermal actuator. The thermal actuator is coupled to an optical mirror. Both the thermal actuator and the optical mirror are disposed on a surface of a substrate. The thermal actuator has multiple beams. A first end of each beam is coupled to the optical mirror. A second end of each beam is attached to the substrate surface.
Each beam of the thermal actuator has two material layers stacked one upon the other. The stacked material layers each have a different coefficient of thermal expansion.
The thermal actuator mechanically moves the optical mirror in response to a current being applied to the beams. Applying the current to the beams heats the stacked material layers. As the beams are heated, at least a portion of each beam is heated above the brittle to ductile transition of the material layers, causing a permanent mechanical deformation thereto which remains upon cooling. When the beams deform a first end of each beam as well as the optical mirror coupled thereto lift a predetermined height above the plane of the substrate surface. Such micro-electro-mechanical structures provide a limited range of motion for optical devices coupled thereto which makes them undesirable.
Therefore, micro-electro-mechanical optical devices capable of controlling the movement optical devices coupled thereto continue to be sought.
The present invention is directed to a micro-electro-mechanical structure which controls the movement of an optical device coupled thereto. Both the micro-electro-mechanical structure and the optical device are disposed on a substrate surface. The micro-electro-mechanical structure controls the movement of the optical device by first lifting the optical device a predetermined distance above the plane of the substrate surface. Thereafter, the lifted optical device is moveable relative to the plane of the substrate surface in response to an electrostatic field generated between the electro-mechanical structure and the substrate.
The micro-electro-mechanical structure includes one or more beams disposed on a substrate. A first end of each beam is coupled to the optical device. A second end of each beam is attached to the substrate surface.
The electro-mechanical structure lifts the optical device a predetermined distance above the plane of the substrate surface in response to the application of an activation force. The activation force lifts the first ends of the beams in an upward direction, substantially in an arc, above the plane of the substrate surface. As the first ends of the beams are lifted above the plane of the substrate surface, they also lift the optical device that is coupled thereto.
A variety of activation forces can be applied to the electro-mechanical structure to lift the optical device. Suitable examples include thermal contraction of the beam layers, beam contraction due to intrinsic stress, and electromagnetic forces.
After the optical device is disposed above the plane of the substrate, the optical device moves relative to the plane of the substrate surface in response to an electrostatic field generated between the one or more beams of the electro-mechanical structure and the substrate. The electrostatic field is generated by applying a bias voltage between the beams and the substrate. The electrostatic field deflects the beams as well as the optical device coupled thereto toward the substrate surface. The magnitude of the beam deflection depends on the amount of the applied bias voltage.
The bias voltage that is applied between each beam and the substrate is variable. Varying the voltage applied between each beam and the substrate moves the optical device relative to the surface of the substrate with multiple degrees of freedom. In particular, the multiple degrees of freedom permit both multi-axis movement and translational movement for the optical device.
Both the substrate and the beams are preferably conductive so that the bias voltage may be applied thereto, When either of the substrate or the beams are insufficiently conductive to deflect the beams toward the substrate surface, conductive layers (e. g., electrodes) are optionally formed on regions thereof.
The beams optionally include insulating regions on the undersurface thereof. The insulating regions prevent the beams from shorting to the substrate surface when the bias voltage is applied therebetween.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and do not serve to limit the invention, for which reference should be made to the appended claims.